Does Swift support implicit conversion?

Question

For example, I have the following code:

    let numberOfBlocks = 3
    let blockWidth = SKSpriteNode(imageNamed: "image.png").size.width
    let padding = 20.0

    let offsetX : Float = (self.frame.size.width - (blockWidth * numberOfBlocks + padding * (numberOfBlocks-1))) / 2

I got the error:

'Double' is not convertible to 'UInt8'

Is there a way to implicitly convert the data type (maybe only for primitive data type)?

Edit:

I know how to do the explicit conversion by using constructor of particular type as Iducool suggested. But it's not a big help to my question because we even don't know where to add the conversions. I simplified my expression in playground:

The problem is in "padding" variable, the error message is

'Double' is not convertible to 'UInt8'.

So I did the conversion:

Then the problem is in "blockWidth" variable now.

I added the conversion again:

And error message is:

Type 'UInt8' does not conform to protocol 'FloatLiteralCovertible'

The final working expression is:

Is it simple and swift? I don't think so.

Answer 1

There is no implicitly cast in Swift.

Easy way of conversion in swift is using constructor of particular type.

Like if you want to get Float from double then you can use Float(doubleValue) and Same way if you want to convert float to integer then you can use Int(floatValue).

In your case:

let intValue = UInt8(doubleValue)

Beware that you will lose any value after the decimal point. So, choose a better way. Above conversion is just to help you in understanding.

Note that Swift always chooses Double (rather than Float) when inferring the type of floating-point numbers.

Answer 2

Swift doesn't support implicitly cast anymore in Xcode6 GM. Following answer only apply to Xcode6 beta version.

---

I don't want to talk about implicitly cast is good or bad, but you can have it if you really want with __conversion()

e.g. If you need UInt8 and Int be able to convert from Double

extension Double {
    func __conversion() -> UInt8 { return UInt8(self) }
    func __conversion() -> Int { return Int(self) }
    // add more if you need to
}

---

xcrun swift
Welcome to Swift!  Type :help for assistance.
  1> extension Double {
  2.     func __conversion() -> UInt8 { return UInt8(self) }
  3. }
  4> var d = 1.0
d: Double = 1
  5> var u8 : UInt8 = d
u8: UInt8 = 1
  6>

---

Note: I won't put this in my production code. I only want to point out it if possible but not recommending it.

Answer 3

using bridgeToObjectiveC() method you can call the methods provided in Objective - C to convert from one primitive data type to another for e.g.

variable_name.bridgeToObjectiveC().intValue

will convert that variable named variable_name to integer

Answer 4

Implicit conversion is possible but with literals only and some conversions are available from the box e.g. Int -> Double:

let a = 3 // Int
let b = 100.5 // Double

// Doesn't work with variables
let c = a * b // Error: Binary operator '*' cannot be applied to operands of type 'Int' and 'Double'

// But this works, because Int(3) literal converts to Double(3.0) implicitly
let d = 3 * b // 301.5

If you want to make backward conversion Double -> Int you should extend Int with ExpressibleByFloatLiteral:

extension Int: ExpressibleByFloatLiteral {
    public init(floatLiteral value: Double) {
        self.init(value)
    }
}

// Double(100.5) converts to Int(100)
let e = a * 100.5 // 300

Even more it's possible to implicitly convert to any type from literals, for instance String -> URLRequest:

extension URLRequest: ExpressibleByStringLiteral {
    public init(stringLiteral value: String) {
        self.init(url: URL(string: value)!)
    }
}

let request: URLRequest = "https://www.google.com"